Abstract A new technique to directly detect low energy neutral helium has been developed and successfully used in space for the first time. It makes possible the in-situ measurement of the local angular distribution of the flow of interstellar neutral helium in the inner heliosphere. Based on the transformation of a velocity distribution, using Liouville's theorem, a straightforward model has been developed to determine, from these measurements, the flow parameters of the interstellar helium at infinity. From twelve measurements at radial distances between 1 and 5 AU, average values of the flow parameters were determined, namely: υ ∞ = 26 ± 1 km s −1, downstream direction: λ ∞ = 72 ± 2.4°, β ∞ = −2.5 ± 2.7°, temperature T ∞ = 6700 ± 1500 K. These values are in agreement with results found by completely different methods (such as, backscattered UV-light, pick-up ions), although in detail there are significant differences.
The Ulysses neutral gas experiment: Determination of the velocity and temperature of the interstellar neutral helium
Advances in Space Research ; 13 , 6 ; 121-130
1993-01-01
10 pages
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
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